1. Field of the Invention
The present invention relates to an optical multi-axis optoelectronic sensor suitable for use as, for example, a light curtain and an area sensor and, more particularly, to an optical multi-axis optoelectronic sensor, in which an appropriate detection sensitivity can be set according to a distance between sensor heads.
2. Description of the Related Art
An optical multi-axis optoelectronic sensor is generally configured such that a phototransmitting sensor head (i.e., a phototransmitter) having a plurality of phototransmitting elements is arranged on one side while a photoreceiving sensor head (i.e., a photoreceiver) having the same number of photoreceiving elements as that of the phototransmitting elements is arranged on an opposite side. In the case of use as a light curtain, a detection light beam emitted from the phototransmitter is shielded or reflected before the photoreceiver if an object intrudes into a region to be detected (i.e., a dangerous region), so that the intensity of a light beam received by the photoreceiver is partly or wholly varied (in other words, the intensity of a light beam is attenuated), thereby detecting the intrusion of the object. In contrast, in the case of use as an area sensor, either one of optical axes is shielded by an intruding object if the object intrudes into a region to be detected, so that the intensity of a light beam received by one or two or more photoreceiving elements concerned is attenuated, thereby detecting the intrusion of the object into a predetermined region (i.e., a predetermined area).
In the case of an optical multi-axis optoelectronic sensor, since the phototransmitting elements and the photoreceiving elements in the phototransmitter and the photoreceiver, respectively, are integrated with main units (i.e., the phototransmitter and the photoreceiver) when a product is assembled, the intensity of the light beam received by each of the optical axes is liable to be varied, unlike a single optoelectronic sensor or the like. In addition, in order to secure the detection of a greatest distance by the conventional optical multi-axis optoelectronic sensor, it is general that all of the phototransmitting elements are made to emit the light beams in the maximum rated intensity of the light beam substantially irrespective of actual installation environment (i.e., principally, the distance between the sensor heads) while the amplification ratio of an amplifier is made highest on a photoreceiving side, and further, that a photoreceiving judgment threshold is set to a lowest value to such an extent that no erroneous operation can be caused by noise generated inside of a circuit (see, for example, Jpn. Pat. Appln. KOKAI Publication No. 2002-323574).
As described above, since the conventional optical multi-axis optoelectronic sensor has the problem of variations in the intensity of the light beam received by each of the optical axes and the problem of secureness of the greatest detection distance, the phototransmitting intensity, the amplification ratio and the photoreceiving judgment threshold are fixed. Therefore, problems below are pointed out:
(1) detection judgments by other adjacent optoelectronic sensors are liable to be adversely affected by the high phototransmitting intensity; and
(2) a light beam shielding state is liable to be erroneously judged as a light beam incident state in a situation in which light beams detected by other optoelectronic sensors are incident into its own photoreceiving elements since the photoreceiving signal amplification ratio is high and the photoreceiving judgment threshold is small.